1. Field of the Invention
The present invention relates to improvements of so-called CTP (Computer to Plate) machines for directly forming desired drawings on form plates by operating laser-beam scanning heads with drawing image signals sent from computers; which CTP machines are used to make printing plates for newspaper printing and the like.
2. Prior Art
Because use of computers in the information processing art, or image processing art, has increased in recent years, a printing plate making machine for a CTP-system for making printing plates for newspaper printing has been developed and put to practical use. This printing-plate-making machine forms a drawing directly on a plate with a laser beam in accordance with drawing image signals sent from a computer.
For news printing however, it is very important to improve printing efficiency because it is often required that great numbers of newspapers be printed in short times. In order to print a great number of newspapers in a short time, in accordance with such requirements, it is necessary to further decrease a time of "stop of operation" of a rotary press for carrying out so-called printing plate replacement. For example, it is necessary to decrease a number of printing plates to be replaced by increasing the size of the printing plates. Thus, the time required for printing-plate setting can be decreased by decreasing the number of printing plates to be replaced.
However, if the size of the plates is increased, for example the plate equivalent of one page of newspaper (lateral width W.times.length L) could be changed to be a plate equivalent of two pages of newspaper (lateral width W.times.length 2L), the required time for producing one printing plate is increased from approximately 4 minutes (in the case of one page) to approximately 5 minutes 30 seconds (in the case of two pages) because the drawing area of the plate increases.
As a result, even if the printing plate setting time required for printing-plate replacement can be approximately halved by increasing the size of printing plates (e.g. double size), supplying the printing plates is restricted due to speed restrictions in producing the printing plates and therefore, the problem occurs that equipment for producing the printing plates must be greatly enlarged.
To solve the above problems, the present applicant previously developed the machine shown in FIGS. 9-11 and a method disclosed in Japanese Patent Application No. 222141/1995 for producing printing plates for newspaper printing.
FIG. 9 is an exterior view of a machine for producing printing plates for newspaper printing in which a dark-room section F, a plate feed section A, an exposure section B. a plate discharge section C, a development section D, and a printing plate storage section E are basically provided along a longitudinal direction of a machine body K. Moreover, though not illustrated, laser-beam scanning heads are operated with so-called image signals sent to the exposure section B from a computer provided at a separate control section and laser scanning corresponding to the image signals is applied to OPC layers of OPC (organic Photo Conductor) plates, and thereby image-signal drawings are drawn on plate surfaces as electrostatic latent images.
FIGS. 10 and 11 are respective top and side views showing outlines of the arrangement of the plate feed section A, the exposure section B, and the plate discharge section C of the machine of FIG. 9 for producing printing plates for newspaper printing.
The plate feed section A comprises a stocker case 1, a vacuum-type sucker 2, a transfer unit 3, and a guide rail 4. OPC plates P, each provided with an organic photo conductor layer and being stored in the stocker case 1, are transferred to the exposure section B by the transfer unit 3 one by one.
A plurality of plates P are superposed on one another, being packed with slip sheets for protecting surfaces of the form plates between them. The packed plates P are unpacked in the dark-room section F and the slip sheets are removed from between them and thereafter, only the plates P are superposed in the stocker case 1. The stocker case 1, in which the form plates P are superposed, is at a predetermined position in the plate feed section A relative to the dark-room section F.
The exposure section B (there are actually two sub-exposure sections B1 and B2), comprises a table 5 (5a and 5b), an exposure barrel 6 (6a and 6b), a roller 7 (7a and 7b), and a laser-beam scanning head 8 (8a and 8b). In the case of this machine H for producing the printing plates for newspaper printing, the two sub-exposure sections B1 and B2 are provided to expedite production of the printing plates, the two sub-exposure sections being spaced an interval along the longitudinal direction of the machine body K from one another, the exposure barrel of each being rotatable about its laterally positioned axis.
Moreover, two laser-beam scanning heads 8 (8a1, 8a2 and 8b1, 8b2) are arranged at each sub-exposure section B1 and B2. By synchronously operating these two laser-beam scanning heads, a drawing is formed on the plates P at a speed two times higher than when only one laser-beam scanning head 8 is used.
The plate discharge section C comprises a discharge table 9 provided between the exposure section B and the development section D. Exposed plates P transferred from each sub-exposure section B1, B2 by the transfer unit 3 are discharged onto the plate discharge section C and subsequently sent to the development section D.
In FIG. 11, a plate P transferred onto the table 5a via a route R.sub.1 by the transfer unit 3 is wound about the first exposure barrel 6a by a counterclockwise rotation of the roller 7a and a clockwise rotation of the first exposure barrel 6a and then, the laser-beam scanning head 8a is operated, thereby making a drawing corresponding to a drawing image signal output from the computer section (not shown)
When predetermined laser-beam scanning is completed, the roller 7a and the first exposure barrel 6a are respectively rotated in opposite directions, and the exposed plate P is discharged temporarily onto the table 5a. Then, the exposed plate P is transferred onto the discharge table 9 by the transfer unit 3 via a route R.sub.2 and the transfer unit 3, having released the plate P, is returned to the stocker case 1 via a route R.sub.3.
The same operation is also performed at the second exposure barrel 6b, with a new plate P being transferred onto the table 5b via a route R.sub.4 while a drawing on the plate P is being made at the first exposure barrel 6a. When a drawing at the second exposure barrel 6bis completed, the exposed form plate P is transferred onto the discharge table 9 from the table 5b via a route R.sub.5. Operations of the first exposure barrel 6a, the second exposure barrel 6b and the transfer unit 3 are sequentially performed in accordance with a predetermined timing program and the exposed plates P are thus alternately sent into the development section D from the exposure barrels 6a and 6b.
Problems to be Solved by the Invention
The machine for making the printing plates for newspaper printing shown in FIGS. 9-11 requires the following time to process a plate P for one page of newspaper with one operating laser-beam scanning head.
______________________________________ Time for drawing by rotation Approximately 153 sec. of exposure barrel Time for placing the plate Approximately 13 sec. on the exposure barrel Time for removing the plate Approximately 13 sec. from exposure barrel Time for transferring the Approximately 15 sec. plate (Route R.sub.1) Time for transferring the Approximately 15 sec. exposed plate (Route R.sub.2) Time for allowing transfer Approximately 15 sec. unit to return (Route R.sub.3) ______________________________________
That is, because the tables 5a and 5b are used to hold the plates P before their engagement with the exposure barrels 6a and 6b and also to hold the plates P after their removal from the exposure barrels 6a and 6b, it is impossible to transfer new plates P to the exposure barrels 6a and 6b until the old plates P, which have been removed from the exposure barrels 6a and 6b have been transferred from the tables 5a and 5b to the discharge table 9. As a result, an amount (approximately 45 seconds) of the total operation time of the transfer unit 3 in the preceding exposure operation for one exposure barrel 6 is so-called waiting time in which operation of the exposure barrel 6 is suspended. Even if drawing time is shortened by using a plurality of laser-beam scanning heads 8, there remains the problem that it is impossible to greatly shorten the overall time for making printing plates because the time for waiting for new (or next) plates P is relatively long and it is impossible to quickly feed the next plates P.
It is an object of the present invention to solve the above problem of the machine shown in FIGS. 9 to 11 for making printing plates for newspaper printing and to provide a machine for making printing plates for newspaper printing which, without an increase in size and manufacturing costs of the machine, can greatly increase the speed of making the printing plates.